Volt-ampere meter



M 30, 1944- 1. F. KlNNA-RD 2,350,170

VOLT AMPERE METER Filed Oct. 15, 1941 Inventor: Isaac FT Kinnamd,

His Attorney.

Patented May 30, 1944 VOLT-AMPERE METER Isaac F. Kinnard, Boston, Mass.,assignor to General Electric Company, a corporation of New YorkApplication October 15, 1941, Serial No. 415,059

8 Claims. (Cl. 171-95) My invention relates to the measurement of voltamperes and in particular it relates to a thermal volt ampere demandmeter. .In carrying my invention into effect, I provide differentialmeasuring instruments such as a meter having two torques which opposeeach other. These torques are produced in response to the flow of theload current of the circuit, the volt amperes of which are to bemetered, and the ratio of the two torques is varied in such a way inresponse to changes in voltage of the circuit to be metered that theresultant torque is proportional to volt amperes. In a preferredarrangement the load current is caused to flow in parallel torqueproducing meter circuits, one circuit producing a relatively largepositive torque and the other a relatively small negative torque, thetwo torques operating upon the same measuring element so that itresponds to the difference in the torques.

The circuit supplying the negative torque contains a regulatorcontrolled by the voltage which reduces the relative amount ofcurrentflowing in such negative torque producing circuit as the voltageincreases by an amount which causes the differential torque to besubstantially proportional to volt amperes.

The features of my invention which are be- I lieved to be novel andpatentable will be pointed out in the claims appended hereto; For abetter understanding of my invention reference is made in the followingdescription to the accompanying drawing in which Fig. i represents anembodiment of my invention employing thermal torque producinggelements,with a voltage responsive regulator in the negative torque producingcircuit. Fig. 2 represents a schematic modification where the voltageresponsive regulator operates differentially on both the negative andpositive torque producing circuits. Fig. 3 represents an indicating voltampere meter embodying my invention.

Referring now to Fig. 1, It represents a power line which may be eitherD. C. or A. C. but

since the problem of measuring volt amperes is bothersome only inconnection with alternating current circuits, my invention is notlimited to, but is intended to be used for, measuring the volt amperesof alternating current circuits. II represents a current transformer forobtaining a current proportional to the load current of power line I0.The current transformer energizes reverse torque elements of a thermaltype of meter which elements are supplied fromthe secondary oftransformer II in parallel. The thermal meter comprises a shaft I2 ofconducting material to which is fastened the inner ends of three spiralsI3, I4 and I5. The central spiral I4 is not of bimetal and produces notorque changes on shaft I2 by reason of changes in temperature. Itserves with shaft I2 as a common current connection to the inner ends ofspirals I3 and I5 and is thus connected to one side of the secondary ofthe current transformer by lead I6. Also, the outer end of spiral I4-maybe adjustable for the purposes of adjusting the zero setting of themeter. Shown in dotted line outline is a shell Il encasing the meter andthe clip I8 is intended to secure the outer end of spiral It to a slotIla in the shell H in order that the outer end of spiral It may besecured in a fixed but adjustable position about shaft I2. Spirals l3and I5 are of bimetal, the inner side of which has a temperaturecoefficient of expansion greater than the outer side so that when thesespirals, are heated they tend to uncoil. Their outer ends are suitablysecured so as to remain stationary, for example to the shell I1, andhence expansion'and contraction of spirals I3 and I5 producetorquestending to rotate shaft l2. These thermal responsive spirals are coiledabout the shaft in opposite directions and hence produce reverse torqueson shaft l2. Thus spiral I3 tends to rotate shaft I2 counterclockwisewhen heated and spiral I5 tends to rotate shaft l2 clockwise whenheated. These thermal responsive spirals are heated by current flowtherethrough and thus comprise their own heaters, although separateheaters might be used if desired. The outer ends of spirals l3 and I5are connected to the other lead IQ of the secondary of currenttransformer II, spiral I3 directly and spiral I5 through a resistance 20andwires II and 22.

It is thus seen that the spirals l3 and I5 are connected in parallel tothe secondary of transformer II, the connection of spiral I3 beingthrough lead I6, shaft I2 and lead I9 and the connection of spiral I5being through lead I6, shaft I2, wire 2|, resistance 20, wire 22, andlead 19. Generally the greater amount of current passes through spiralI3 and it produces the greater torque. Avariable amount of the totalline current is shunted about spiral I3 through what may be termed thereverse torque spiral I5 and resistance 20. In order to vary 1 thecurrent through spiral I5 and hence the enclosing tube 23. eitherevacuated or gas filled,

containing the resistance 20 and a heater resistance 24 which isconnected across the secondary of a potential transformer 25 suppliedfrom the voltageof line I. Suitable leading-in wires are provided forthe tube 23 as shown. It is 'now seen that heater 24 is energized inproportion to the voltage of line l0. Resistance 20 is made of amaterial having a positive temperature coeflicient of resistance andhence its resistance increases with rise in voltage of line I. I havefound that it is satisfactory to make the shunt resistance 20 of ironwire and preferably operate it between temperatures of 100 to 500degrees C. in the tube which reduces heat losses and prevents oxidationof the resistance 20 and heater 24.

Other materials having high temperature coefiicients of resistance mayalso be used for the resistance 20. It is desirable, however, to employa material which has a large temperature coeflicient of resistance and atemperature coefiicient which is either substantially constant orincreases with temperature over the temperature range at which it willoperate, taking into consideration not only changes in voltage but alsochanges in ambient temperature. For

7 example, nickel might be usedup to about-100 C. If the operatingtemperature goes above 1000 .C. a tungsten resistor could be used.

It is seen thairI have provided a metering device operated by the loadcurrent and Jointly controlled by the load current and the voltage ofthe line l0. Two torques are produced. a torque T in one directionproduced by spiral l3 and a smaller torque't in the opposite directionproduced by spiral ii. The resultant torque T-t causes rotation of shaftl2 and it is possible by the arrangement described to produce aresultant torque and deflection substantially proportional to voltamperes. The regulation is independent of variations in the power factoror .the phase relation betweeen the load and voltage currents.

The rotary movement of shaft l2 which occurs in response to thedifferential torque of spirals l3 and I5 is conveyed to a shaft I20.through deflection multiplying gears 23 and moves a pointer 21 over avolt ampere scale 28. A friction pointer 29 may also be provided whichis pushed upscale by pointer 21 to remain at the highest point ofdeflection to indicate the maximum volt ampere demand. v

Assume now that for a given line current and normal voltage a givenpointer deflection is produced by reason of the factthat the torque of 1spiral l3 exceeds that of a spiral I5. If, now, the

voltage increases, the resistance 20 in the reverse torque branch of thecircuit is increased. Hence more current will flow through spiral l3 andless through spiral I5, resulting in an increased deflection. If thevoltage decreases below normal,

resistance 20 will operate at a lower than normal temperature and itsresistance will be less than normal. Hence the torque of spiral l5 willinreason of the current flow theretlu'ough should be negligible ascompared to heating produced by the voltage heater 24. It is possiblethus .to arrange matters to obtain a measurement approximatelyproportional to volt amperes over the useful measurement range.

In a practicable meter it has been found that,

under normal operating conditions, that is'full of spirals l3, l5 andresistor 20 may be in the relation of .05, .05 and .035 ohm withresistor 20 operating at a. considerably higher tempera- .ture thanspirals l3 and I 5. The invention,

however, is not confined to this resistance relationship or to thevalues specified. The particular type of thermal meter represented is ofthe type described in detail in a copending applica-' tion of Edward E.Lynch and Herbert -C. Thomas-Serial No. 398,602, filed June 18, 1941,

and assigned to thesame assignee as the present invention.

' In Fig. 2 I have schematically represented a modification which may bethe same as that of Fig. 1 with the following exception. The posi; tivetorque spiral l3 also has in series with'it a temperature sensitiveresistance 30. This resistor 30 is contained within the tube 23 heatedby the voltage heater 24. However, resistor 30 has a negativetemperature coeflicient of resist ance instead of a positive temperaturecoefllcient of resistance. In such an arrangement the resistor 30differentially assists resistor 20 in the regulation in responsetovoltage to shift cur-v rent from negative torque spiral I5 to positivetorque spira.l l3 in response to a rise in voltage. The resistances andresistance changes will be so chosen as to obtain a resultant responseproportional to volt amperes.

. In Fig. 3 I have shown a further modification of my invention whichhas very little thermal and time lag between a circuit changingcondition and the measurement response. In Fig. 3, l0 represents the A.C. line being metered and II the current transformer which suppliescoils 3| and 32 of an iron vane ammeter in parallel circuits. Coils 3|and 32 are connected in opposition and coil 3| predominates to producethe contains a filament like resistance 38' which is crease relative tothe torque of spiral |3"and a decreased deflection will result.Theoretically the torques of spirals l3 and I5 should be equal whenthere is no heating of resistor 20 by heater 24 corresponding to a zerovoltage condition. Actually such a condition will not arise in practiceand it is generally suflicient to have the voltage regulator perform itsfunction over a voltage range from 10% above to 10% below heated inresponse to the voltage of line l0. Expansion chamber 35 has no heaterand hence as the voltage'increases and the gas in chamber 34 expandsrelative to that in chamber 35, the mercury level in the two risers ofthe U tube will shift accordingly.

Such shift in mercury level is used to differentially controlresistances 40 and 4| contained in the circuits of "coils 3| and 32respectively. Hence, when the voltage increases, resistance 4| isincreased and resistance 40 is decreased, and accordingly current incoil 3| increases at the ex pense of a decrease in current in coil 32.As

a result, the differential or operating flux of the meter varies inproportion to the. linevoltage changes as well as line current and bysuitably selecting the resistance and adjusting the voltage current inthe heater circuit-by an adiustable resistance 42 the meter deflectionmay .be

. made proportional to volt-'amperes over the use-' .normal voltage.Heating of resistance 20 by 1 ful measurement range.

Any suitable form ofdiiierential ,A. C. am-"' meter, including thethermal meter previously described, may be used. Since the two chambersIt and II are substantially equally influenced by ambient temperaturechange the regulator tends to be sell-compensated ior ambienttemperature variations, as is also true of the other modifications.

In accordance with the provisions oi the patent statutes, I havedescribed the principle of operation or my invention together with theapparatus which I now consider to represent the best embodiment thereof,but I desire to have it understood that the apparatus shown is onlyillustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent the UnitedStates, is:

1. Apparatus for measuring the product of the volt and ampere quantitiesof an electric power line comprisinga diflerential electrical measuringinstrument having a pair of energizing cir-.

cuits and responsive to the difference of the flow 01.current in saidenergizing circuits, means for energizing said circuits in parallel byin-phase alternating currents, the total of which is proportional to oneoi said quantities, and a regulator responsive to the other or saidquantities for varying the relative flow of such currents in theparallel energizing circuits independently of variations in the phaserelation between the volt and ampere quantities such that the responseof the diil'erential instrument is substantially proportional to thevolt amperes of the line to be metered;

2. A volt amperemeter comprising a diiierential electrical indicatinginstrument having a pair of energizing circuits and responsive to thediilerence in the flow of current in said circuits, means for energizingboth of said circuits by inphase alternating currents, the sum. 0! whichis proportional tothe current of the circuit the volt amperes of which'are to be measured, and a regulator responsive to the voltage of thecircuit to be metered for varying the relative flow 01' such currents insaid circuits independently of variations in the phase relation betweenthe current and voltage of the circuit to be metered such that theindicating response of said instrument is substantially proportional tothe volt amperes of the circuit to be metered.

3. Apparatus for obtaining a measurement proportional to volt amperes ofan alternating current circuit comprising a measuring instrument havingtwo energizing circuits and influenced in response to the diflerentialflow of inphase alternating current in such energizing circuits,connections for causing a current the total of which is proportional tothe current of the circuit to be metered to divide and flow in parallelin said energizing circuits, and a regulator in at least one of saidparallel circuits controlled in response to the voltage of the circuitto be metered independently of variations in the phase relation betweenthe current and voltage of the metered circuit for varying the relativemagnitude of such currents flowing in the two parallel circuits suchthat the differential response of said instrument is substantiallyproportional to the volt ampere of the circuit'to be metered.

4. Apparatus for measuring the volt amperes of an electriccircuitcomprisinga measuring instrument having two energizing circuitsand responsive to the diilerence oi the flow oi in-phase alternatingcurrent in said energizing circuits,

substantially proportional to volt amperes.

5. Apparatus ior measuring the volt amperes oi an alternating currentcircuit comprising a dii'ierential electrical measuring instrumenthaving two energizing circuits and. responsive to the diilerentiai flowoi. current in said energizing circuits, connections for causing analternatin current, the total of which is proportional tothe current ofthe circuit to be metered, to divide and flow in parallel in saidenergizing circuits, a regulator comprising means for varying therelative resistances of said twoparallel energizing circuits and athermal means energized in response to the voltage of the circuit to bemetered. for controlling said regulator to cause the diil'erentialresponse oi said instrument to be substantially proportional to voltamperes.

6. Apparatus for measuring the volt amperes of an alternating currentcircuit comprising a diflerential electrical measuring instrument havinga movable indicator and two thermal torque producing devices acting,when heated, in opposition on said movable indicator, electric heatercircuits for the thermal torque producing devices, connections forcausing said heater circuits to be energized in parallel by currents thetotal of which is proportional to the current of the circuit to bemetered, a resistance having a positive temperature coefficient ofresistance in one of said parallel circuits and a heater for saidresistance energized in proportion to the voltage ofthe circuit to bemetered.

7. Apparatus for measuring the volt amperes of an alternating currentcircuit comprising a dii'ierentiaielectrical measuring instrument havinga movable indicator and two thermal torque producing devices which, whenheated, act in opposition" on said movable indicator, electric heatercircuits for said thermal torque producing devices, connections forcausing saidheater circuits to be energized in parallel by currents thetotal of which is proportional to the current in the circuit to bemetered, a resistance having a positive temperature coefllcientoiresistance in one oi said parallel circuits, a resistance having anegative temperature coeflicient oi resistance in the other parallelcircuit and a heater for said resistances energized n roportion to thevoltage oi' the circuit to be metered.

.8. Apparatus for measuring the volt amperes of rim-alternating currentcircuit comprising a diilferential electrical measuring instrumenthaving a movable armature member and two .coils connected in oppositionto produce a diner-

